PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
39 
separate compartment of the annular ligament; it was inserted into the 
second phalanx of the thumb. 
The Extensor brevis pollicis arose from the interosseous membrane 
and from the dorsal aspect of the radius and the ulna, it was inserted 
into the radial aspect of the base of the first metacarpal bone well to 
the anterior surface. This muscle is absent in most apes. Langer, 
Tick, Bischoff, Huxley and Chapman failed to find it in the Orang, 
whilst Hepburn^ describes the muscle as being inserted, as in my 
example, into the metacarpal bone. Bischoff states that the muscle is 
absent in all apes, with the exception of the Gorilla. The muscle in 
my Orang was quite separate from the extensor ossis metacarpi pollicis, 
and had a distinct and separate insertion into the metacarpal bone. It 
represents a condition intermediate between that normal in man and 
that which Testut says is^ constant in most apes where, according to 
this authority, the short extensor is blended with the extensor ossis 
metacarpi pollicis. 
The Extensor ossis metaca7pi pollicis arose from the radius and ulna, the 
more extensive attachment being to the radius, and was inserted by two 
tendons, one of which passed to the trapezium and the other to the 
fascia, from which the abductor pollicis and opponens arose. On the 
right side Rudolf found this tendon passing to the metacarpal bone 
of the thumb. On close examination of the slip to the trapezium one 
found, close to the point of insertion, a small irregularly oval sesa- 
moid bone about 4 mm. in length. This bone was embedded in fibrous 
tissue which extended from the styloid process of the radius above to 
the base of the first metacarpal bone, and was there closely applied to 
the trapezium immediately below the tubercle of the scaphoid ; the 
fibres of the tendon of the muscle appeared to be inserted into this bone. 
The sesamoid bone is described by Fick^ and by Hepburn^ in con- 
nection with the tendon of the extensor ossis metacarpi pollicis in the 
Orang. Fick describes the muscle as inserted into the trapezium 
and the first metacarpal on the left side, whilst it had an additional 
insertion into the scaphoid on the right side of his Orang. Bischoff^ 
states that in the Orang, Cynocephalus, Pithecia and Hapale, the muscle 
is inserted as in man, into the metacarpal bone, whilst in the Gorilla, 
1 Loc. cit., p. 167. 
2 Loc. cit. I, Vol, I, pt. 2, p. 81 1. 
3 Loc. cit. I, p. — , 
4 Loc. cit., p. 167. 
5 Loc. cit. I, p. 213. 
